The present invention relates to impact attenuation.
Impact attenuation devices according to the invention may be incorporated in many different products for absorbing shock loads from impacts. In automobiles, devices according to the invention may be incorporated into doors to absorb side impacts and into the front and rear ends to absorb energies involved in front and rear end crashes. In sports equipment, the invention may be used, for example, in sporting helmets.
According to the present invention there is provided an apparatus for attenuating shock loads, comprising:
a flexible, non-rigid, outer envelope with opposite, spaced apart first and second sides and a peripheral wall extending between the first and second sides;
an inner baffle extending across the envelope, the baffle being positioned between and spaced from the first and second sides and having a periphery secured to the peripheral wall of the envelope so as to separate the interior of the envelope into chambers on opposite sides of the inner baffle, the inner baffle comprising a flexible, non-rigid material of high strain resistance; and
gas inflating said envelope to a superatmospheric pressure wherein:
the outer envelope is formed from a material of high strain resistance that is impervious to said gas; and
the inner baffle is formed from a flexible, non-rigid material of high strain resistance that is pervious to said gas, whereby:
a shock load on one of said first and second sides will produce an increased gas pressure between the baffle and said one of said first and second sides above said superatmospheric pressure and gas will permeate through the baffle to reduce the increased gas pressure.
The gas flow through the pervious baffle dissipates energy, spreading the load over the second side of the envelope and causing a time delay in the build-up of pressure on the second side. In preferred embodiments of the invention, there are plural, parallel baffles in the envelope to provide a multi-stage energy dissipation.
The outer envelope is preferably made from a high tensile strength woven fabric with an impervious inner coating. Exemplary materials are a fabric woven from para-amide fibres such as those sold under the trademark xe2x80x9cKEVLARxe2x80x9d. The impervious coating may be a polyurethane coating, with additional sealing material used as necessary, for example to seal seams. The baffle may be made of a fabric woven from the same material, but uncoated to provide the desired permeability. The pattern and tightness of the weave will alter the permeability properties and thus the rate at which gas will pass through the baffle. These characteristics may used to vary the shock attenuation properties of the apparatus.
The gas used in the envelope is preferably nitrogen. For manufacture, liquid nitrogen can be poured into the envelope. When the envelope is sealed closed, the nitrogen is allowed to evaporate, inflating the envelope. This avoids the use of high pressure injection valves.
The maximum impact that can be absorbed by a device according to the invention is a function of the internal pressure at which the envelope will rupture. The ultimate rupture strength can be increased by adding fabric jackets to the outside of the envelope. These fit over the envelope like a pillow case. The jackets are preferably made of the same high strength textile fabric as the envelope.
Because the device is made from cloth, it can be made in almost any desired shape. For contoured shapes, ties may be used between the opposite sides, varying the maximum spacing between the sides.
The apparatus may also be rechargeable. It can be refilled with gas to compensate for leakage over time. This is particularly easy if the gas is introduced as a liquid.
As noted above, the apparatus may not use a pressure valve. Instead, a neck may be formed on the outer envelope. This can be used as a port providing access to the interior of the envelope for sealing the final seam of the envelope during manufacture. It is also used as a port into which liquid nitrogen is poured. When the liquid is in the envelope, knots are tied in the neck to close off the egress for gas as the liquid vaporizes.